WO2025197272A1 - Composition for aqueous coating material using polyester resin - Google Patents

Abstract

Provided are: a composition for an aqueous coating material that comprises a polyester resin and inorganic particles, the composition having excellent adhesiveness and easy peelability with respect to a polyester base film, antifogging properties, and blocking resistance; a laminate; and a packaging material. The composition for an aqueous coating material contains a polyester resin (A) satisfying the following conditions and inorganic particles (B): (i) among the polycarboxylic acid components constituting (A), aromatic polyvalent carboxylic acid components having no sulfonic acid groups constitute 60-88 mol% of said polycarboxylic acid components, aromatic polyvalent carboxylic acid components having a sulfonic acid group constitute 8-20 mol% of said polycarboxylic acid components, and aliphatic polyvalent carboxylic acid components and/or alicyclic dicarboxylic acids constitute 5-20 mol% of said polycarboxylic acid components; (ii) among the polyhydric alcohol components constituting (A), glycols containing an ether group constitute more than 50 mol% of said polyhydric alcohol components; and (iii) the glass transition temperature of (A) is less than 20° C.

Description

Water-based coating composition using polyester resin

The present invention relates to an aqueous coating composition that uses a polyester resin with excellent water-dispersibility. More specifically, it is an aqueous coating composition whose main component is a polyester resin that has extremely high hydrophilicity and water-dispersibility, and which, when formed into a coating film, has high adhesion, easy peelability, and anti-fogging properties.

Polyester resins are widely used as raw materials for resin compositions used in paints, coatings, adhesives, etc. Polyester resins are generally composed of polycarboxylic acids and polyhydric alcohols. By selecting and combining the polycarboxylic acids and polyhydric alcohols, the molecular weight can be freely controlled, and the resulting polyester resins are used in a variety of applications, including paints and adhesives.

In the molecular design of polyester resins, the selection of copolymerization components is important. Polycarboxylic acid components and polyhydric alcohol components can be broadly classified into aromatic, aliphatic, and alicyclic types. The glass transition temperature (hereafter referred to as Tg), which indicates the flexibility of the polyester resin, can be determined by selecting these components. Generally, polyester resins are used as organic solvent solutions or aqueous dispersions, which are applied to substrates; however, in recent years, environmental concerns have led to a demand for aqueous dispersions. Among these, aqueous dispersions that do not use co-solvents or surfactants are most highly sought after from the perspective of environmental concerns and recyclability.

Furthermore, in recent years, in response to the trend toward mono-materials, lid materials for PET (amorphous polyethylene terephthalate) packaging containers have been used, in which a heat-sealable polyester adhesive composition is applied to a polyester film and then bonded together. There is a demand for polyester coating compositions that can be used for food applications and that combine excellent adhesion, easy peelability, anti-fogging properties, and blocking resistance.

For example, Patent Document 1 proposes a composition comprising a blend of a semi-crystalline polyester resin with a Tg of -30 to 0°C and an amorphous polyester resin with a Tg of 45 to 110°C, to which an anti-fog additive and an anti-blocking agent are added. Furthermore, Patent Document 2 proposes an anti-fog coating agent consisting of a polyester resin, a metal compound, and a surfactant.

Patent No. 7280826 JP 2023-51805 A

However, in Patent Document 1, although the resin composition has anti-fogging properties and high adhesive strength, it is necessary to add an anti-fogging additive other than polyester to impart anti-fogging properties, which poses an issue with recyclability when applied to a PET substrate. Furthermore, in Patent Document 2, it is necessary to add a surfactant in addition to the resin to impart water dispersibility and anti-fogging properties to the resin composition, which also poses an issue with recyclability when applied to a PET substrate.

The present invention was devised in light of the problems with the prior art described above, and its purpose is to provide a water-based coating composition, laminate, and packaging material comprising a polyester resin and inorganic particles that combine excellent adhesion, easy peelability, anti-fogging properties, and blocking resistance, particularly for polyester substrates.

As a result of extensive research to achieve the above objective, the inventors discovered that by combining a polyester resin with inorganic particles of a specific composition, it is possible to obtain a water-based coating composition that can be used in food packaging applications, exhibits excellent adhesion to A-PET containers, and, because the resin itself possesses excellent water dispersibility and anti-fogging properties, does not require co-solvents, surfactants, or anti-fogging agents, leading to the completion of the present invention.

In other words, the present invention comprises the following components (1) to (9).

(1) A water-based coating composition containing a polyester resin (A) and inorganic particles (B), wherein the polyester resin (A) satisfies the following conditions (i) to (iii):
(i) Among the polycarboxylic acid components constituting the polyester resin (A), the polyester resin (A) contains 60 to 88 mol % of an aromatic polycarboxylic acid component having no sulfonic acid group, 8 to 20 mol % of an aromatic polycarboxylic acid component having a sulfonic acid group, and 5 to 20 mol % of an aliphatic polycarboxylic acid component and/or an alicyclic dicarboxylic acid;
(ii) the polyhydric alcohol component constituting the polyester resin (A) contains more than 50 mol% of a glycol containing an ether group;
(iii) The glass transition temperature of the polyester resin (A) is lower than 20°C.
(2) The aqueous coating composition according to (1), wherein the polyester resin (A) has a reduced viscosity of 0.2 to 0.7 dl/g.
(3) The aqueous coating composition according to (1), wherein the inorganic particles (B) have a particle size of 1 to 30 μm and a pore volume of 2 ml/g or less.
(4) The aqueous coating composition according to (1), which does not contain a curing agent.
(5) A laminated film characterized by being constructed by applying the aqueous coating composition according to any one of (1) to (4) to at least one surface of a thermoplastic resin film.
(6) The laminated film according to (5), wherein the thermoplastic resin film is a PET film.
(7) A packaging material having the laminated film according to (6) as a component.
(8) A lid material for a food packaging container, having the packaging material according to (7) as a component.
(9) A food packaging container having the lid material according to (8) as a component.

The aqueous coating composition of the present invention has anti-fogging properties and exhibits high adhesion to PET while being easily peelable. This makes it suitable for use as a heat-sealable layer in recyclable food packaging containers.

The following describes in detail the embodiments of the present invention.

The aqueous coating composition of the present invention contains a polyester resin (A) that meets specific requirements and inorganic particles (B).

<Polyester Resin (A)>
The polyester resin (A) has a chemical structure that can be obtained by polycondensation of a polycarboxylic acid component and a polyhydric alcohol component, and the polycarboxylic acid component and the polyhydric alcohol component each consist of one or more selected components.

The polycarboxylic acid component constituting polyester resin (A) may be an aromatic carboxylic acid, an alicyclic polycarboxylic acid, and/or an aliphatic polycarboxylic acid, with aromatic dicarboxylic acids and aliphatic dicarboxylic acids being preferred.

Among the polycarboxylic acid components, the aromatic polycarboxylic acid component without sulfonic acid groups is contained in an amount of 60 to 88 mol%, preferably 65 to 85 mol%, and more preferably 70 to 80 mol%. If the aromatic polycarboxylic acid component without sulfonic acid groups is less than this range, the adhesive strength of the coating film will decrease, and if it is more than this range, the substrate may be destroyed when peeled off.

Examples of the aromatic polycarboxylic acid component that does not have a sulfonic acid group include aromatic polycarboxylic acid components such as terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, phenylenedicarboxylic acid, trimellitic acid, pyromellitic acid, benzophenonetetracarboxylic acid, and alkali metal salts thereof. While one or more of these can be used, it is preferable to use isophthalic acid from the perspective of water dispersibility. Furthermore, to prevent gelation during synthesis, it is preferable that the content of trifunctional or higher aromatic polycarboxylic acid components be 3 mol% or less.

Among the polycarboxylic acid components, 8 to 20 mol %, preferably 10 to 15 mol %, of an aromatic polycarboxylic acid component having a sulfonic acid group is contained. If the aromatic polycarboxylic acid component having a sulfonic acid group is contained in an amount less than the above range, the water dispersibility of the resin may decrease, and if it is contained in an amount greater than the above range, the water resistance of the resin may decrease.

Examples of the aromatic polycarboxylic acid component having a sulfonic acid group include 5-sulfoisophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, 5-[4-sulfophenoxy]isophthalic acid, and alkali metal salts thereof. These can be used alone or in combination.

Among the polycarboxylic acid components, the content is 5 to 20 mol %, preferably 6 to 18 mol %, and more preferably 10 to 15 mol % of an aliphatic polycarboxylic acid component and/or an alicyclic polycarboxylic acid component. If the content of the aliphatic polycarboxylic acid component and/or the alicyclic polycarboxylic acid component is less than the above range, the water dispersibility of the resin may decrease, and if it is more than the above range, the moisture resistance of the resin may decrease. The aliphatic polycarboxylic acid component and/or the alicyclic polycarboxylic acid component preferably does not have a sulfonic acid group.

Examples of the aliphatic polycarboxylic acid component include succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, fumaric acid, maleic acid, itaconic acid, and citraconic acid. Examples of the alicyclic polycarboxylic acid include 1,4-cyclohexanedicarboxylic acid, tetrahydrophthalic acid, hexahydroisophthalic acid, 1,2-cyclohexenedicarboxylic acid, and 2,5-norbornanedicarboxylic acid. These can be used alone or in combination.

Among the polyhydric alcohol components, it is preferable to contain more than 50 mol% of a glycol containing an ether group, such as diethylene glycol. This is preferably 55 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 80 mol% or more, and 100 mol% is acceptable. A content of more than 50 mol% of the above-mentioned glycol containing an ether group improves the water dispersibility of the resin, which is preferable. In terms of moisture resistance, it is preferable to blend components other than the above-mentioned glycol containing an ether group at 50 mol% or less. Among the glycols containing ether groups, diethylene glycol is particularly preferable, as it does not bias the hydrophilic portion of the resin skeleton and improves moisture resistance due to hydrolysis.

Among the polyhydric alcohol components, examples other than diethylene glycol include aliphatic glycols such as ethylene glycol, 1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 1,4-butanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,8-octanediol, 3-methyl-1,6-hexanediol, 4-methyl-1,7-heptanediol, 4-methyl-1,8-octanediol, and 1,9-nonanediol; alicyclic glycols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane glycols, and hydrogenated bisphenols; and polyether glycols such as triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. These can be used alone or in combination.

Furthermore, to impart an acid value, acid anhydrides such as trimellitic anhydride and pyromellitic anhydride may be added (post-added) after polymerization of polyester resin (A). Specific examples of acid anhydrides for imparting an acid value include trimellitic anhydride, pyromellitic anhydride, and ethylene glycol bisanhydrotrimellitate, and one or more of these may be used. When added (post-added), the total amount of the polycarboxylic acid component and polyhydric alcohol component may exceed 200 mol%. In this case, the total amount of the composition excluding the component to which the acid anhydride or the like has been added (post-added) is considered to be 200 mol% in the calculation.

When producing polyester resin (A), polymerization catalysts that can be used include, for example, titanium compounds such as tetra-n-butyl titanate, tetraisopropyl titanate, and titanium oxyacetylcetonate; antimony compounds such as antimony trioxide and tributoxyantimony; germanium compounds such as germanium oxide and tetra-n-butoxygermanium; and acetates of magnesium, iron, zinc, manganese, cobalt, and aluminum. These catalysts can be used alone or in combination of two or more.

The method for producing polyester resin (A) is not particularly limited, but examples include: 1) a method in which a polycarboxylic acid and a polyhydric alcohol are heated in the presence of an arbitrary catalyst, followed by a dehydration esterification step and then a polyhydric alcohol removal/polycondensation reaction; and 2) a method in which an alcohol ester of a polycarboxylic acid and a polyhydric alcohol are heated in the presence of an arbitrary catalyst, followed by a transesterification reaction and then a polyhydric alcohol removal/polycondensation reaction. In methods 1) and 2), some or all of the acid components may be replaced with acid anhydrides.

The glass transition temperature (Tg) of the polyester resin (A) is less than 20°C, preferably -15°C or higher and lower than 20°C, and more preferably -10°C or higher and lower than 20°C. A Tg of less than 20°C is preferable, as this improves ease of opening when the coating composition of the present invention is used as a container closure material. A Tg of -15°C or higher is preferable, as there is no risk of blocking occurring during the preparation of the coating composition.

The reduced viscosity (ηsp/c) of polyester resin (A) is preferably 0.2 to 0.7 dl/g. More preferably, it is 0.3 to 0.6 dl/g. By setting it at or above the lower limit, the resin cohesive strength is improved, allowing for excellent adhesive properties to be achieved. Furthermore, by setting it at or below the upper limit, water dispersibility is improved. The reduced viscosity can be adjusted as desired by changing the polymerization time, temperature, and degree of reduced pressure during polymerization (in the case of reduced-pressure polymerization) of the polyester resin.

The polyester resin (A) is preferably at least 95% by mass relative to 100% by mass of the solids content of the aqueous coating composition. By making it at or above this lower limit, excellent anti-fogging properties and adhesion can be achieved without the addition of an anti-fogging agent, thanks to the aromatic polycarboxylic acid component having sulfonic acid groups and the glycol containing ether groups, which are the hydrophilic parts of the polyester resin (A).

<Inorganic particles (B)>
The inorganic particles (B) are not particularly limited, but examples thereof include inorganic particles containing oxides, hydroxides, sulfates, carbonates, or silicates of metals such as magnesium, calcium, barium, zinc, zirconium, molybdenum, silicon, antimony, or titanium. Among these inorganic particles, silica particles are particularly preferred. The shape of the particles is not particularly limited and may be any shape, such as powder, granules, granules, platelets, or needles.

The average particle size of the inorganic particles (B) is preferably 1 to 30 μm. It is more preferably 1 to 20 μm, and even more preferably 1 to 12 μm. If the average particle size is below this range, the anti-blocking effect may not be achieved. Furthermore, if the average particle size is above this range, the adhesive strength of the coating film may decrease.

The pore volume of the inorganic particles (B) is preferably 2 ml/g or less, and more preferably 1 ml/g or less. If the pore volume is greater than 2 ml/g, the particles may be destroyed during preparation of the coating composition, and a sufficient anti-blocking effect may not be achieved. From the perspective of achieving an anti-blocking effect, the pore volume of the inorganic particles (B) is preferably 0.1 ml/g or more.

The inorganic particles (B) are preferably less than 5% by mass based on 100% by mass of the solids content of the aqueous coating composition. By making the content less than the upper limit, anti-blocking properties can be exhibited without reducing adhesion. From the perspective of exhibiting anti-blocking effects, the inorganic particles (B) are preferably 0.5% by mass or more based on 100% by mass of the solids content of the aqueous coating composition.

The aqueous paint composition of the present invention is capable of forming a coating film without the addition of a curing agent. Therefore, it is preferable that the paint composition of the present invention contains substantially no curing agent; that is, it is preferable that the curing agent content is less than 1 part by mass (solids content equivalent) per 100 parts by mass (solids content equivalent) of polyester resin (A). By not adding a curing agent, recycling becomes easier when the coating film is formed.

In the aqueous coating composition of the present invention, the content of the curing agent is preferably less than 1 part by mass per 100 parts by mass of the polyester resin (A) (solid content). Less than 0.5 parts by mass is more preferable, less than 0.1 parts by mass is even more preferable, and it is most preferable that no curing agent is contained.

Here, the term "curing agent" refers to a known curing agent that reacts with polyester resin to form a crosslinked structure. Examples of the crosslinked structure include a reaction in which unsaturated double bonds in the polyester resin react through a radical addition reaction, cationic addition reaction, or anionic addition reaction to form an intermolecular carbon-carbon bond, or a condensation reaction with polycarboxylic acid groups or polyhydric alcohol groups in the polyester resin, a polyaddition reaction, or an ester exchange reaction to form an intermolecular bond. Examples of curing agents include phenolic resins, amino resins, isocyanate compounds, epoxy compounds, β-hydroxylamide compounds, and unsaturated bond-containing resins.

In the aqueous coating composition of the present invention, the content of the anti-fog agent is preferably less than 1 part by mass per 100 parts by mass of the polyester resin (A) (solids content). Less than 0.5 parts by mass is more preferable, less than 0.1 parts by mass is even more preferable, and it is most preferable that the composition does not contain any anti-fog agent.

Here, examples of anti-fogging agents include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants.

<Laminated film>
The laminate film of the present invention is constructed by applying the aqueous coating composition to at least one surface of a thermoplastic resin film, and in particular, the laminate film of the present invention is obtained by applying the aqueous coating composition to a thermoplastic resin film as a substrate, followed by a drying treatment.

Examples of thermoplastic resin films include polyester-based resin films, polypropylene-based resin films, polyamide-based resin films, polyvinyl alcohol-based resin films, and polyvinylidene chloride-based resin films. Of these, polyester-based resin films, and particularly PET films, are preferred because they are suitable as lid materials for food packaging containers.

The laminated film of the present invention has excellent adhesiveness and anti-fogging properties, making it suitable as a component of packaging materials and blister packs for pharmaceuticals and the like. It is particularly suitable as a lid material for food packaging containers for fresh produce, processed foods such as yogurt, and the like. When used as a lid material for a food packaging container, the contents can be sealed by heat-sealing the coated surface of the laminated film to the food packaging container, and the lid material also has anti-fogging properties. While there are no particular restrictions on the type of food packaging container, polyester-based resins are preferred.

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples. In the examples and comparative examples, parts simply refer to parts by mass.
(Physical property measurement method)

Measurement of the composition of the polyester resin: The molar ratios of the polycarboxylic acid component and the polyhydric alcohol component constituting the polyester resin were determined using a 400 MHz 1H-nuclear magnetic resonance spectrometer (1H-NMR). Deuterated chloroform was used as the solvent.

Measurement of Glass Transition Temperature (Tg) Using a differential scanning calorimeter (DSC) DSC-220 manufactured by Seiko Instruments Inc., 5 mg of a sample (heat-sealable polyester resin) was sealed in an aluminum lid-type container, and measurement was carried out from -100°C to 250°C at a temperature increase rate of 20°C/min. Glass transition temperature (Tg) was determined as the temperature at the intersection of an extension of the baseline below the glass transition temperature and a tangent line showing the maximum slope between the rising part of the peak and the apex of the peak.

Measurement of reduced viscosity (unit: dl/g) The polyester resin was dissolved in a measurement solvent of phenol/tetrachloroethane (mass ratio 6/4) at a sample concentration of 0.1 g/25 ml, and the reduced viscosity was measured at a measurement temperature of 30° C. using an Ubbelohde viscometer.

Evaluation of Water Dispersibility 210 parts by mass of polyester resin and 490 parts by mass of water were mixed and stirred at 80° C. to dissolve, and the dispersion state was evaluated according to the following evaluation criteria.
<Evaluation criteria>
⊚: Disperses in water within 1 hour of stirring without leaving any unemulsified matter. The unemulsified matter referred to here refers to components that settle when the aqueous dispersion is left standing at 25°C for 1 day after preparation.
○: Disperses in water without leaving any unemulsified matter within 1 to 3 hours of stirring. ×: Does not disperse in water or leaves any unemulsified matter even after stirring for more than 3 hours.

Evaluation of Moisture Resistance The polyester resin was stored (left to stand) at 40° C. and 80% RH for 2 weeks, and the reduced viscosity retention rate (before storage/after storage) was confirmed.
<Evaluation criteria>
○: Retention rate 90% or more ×: Retention rate less than 90%

<Average particle size of inorganic particles>
The particle size was measured using a HORIBA LA-750 Particle Size Analyzer. The particle size corresponding to 50 mass percent was read and this value was taken as the average particle size.

<Pore volume of inorganic particles>
The pore volume was determined by measuring the BET nitrogen adsorption isotherm using an AS-1 manufactured by Quantachrome Co., Ltd. Specifically, the pore volume was determined when the relative pressure P/P0 was 0.98.

The aqueous coating compositions obtained in the Examples and Comparative Examples were applied to a 25 μm thick biaxially stretched PET film (Toyobo Ester E5102, manufactured by Toyobo Co., Ltd.) to a thickness of 3 to 4 μm. The film was then dried at 100° C. for 60 seconds to obtain a laminate film.

Blocking Evaluation : The laminated film for evaluation was cut into a 10 cm square, and the coated surface was heat-pressed against a 10 cm square untreated surface of a 25 μm thick A-PET film at a temperature of 45° C. and a pressure of 1.5 MPa for 30 seconds. Blocking was then evaluated by peeling it off by hand.
<Evaluation criteria>
○: Can be peeled off by hand without breaking the material ×: Cannot be peeled off by hand without breaking the material

Anti-fogging evaluation: 100 ml of water at 50°C was poured into a 200 ml mayonnaise bottle, and the laminated film for evaluation was attached to the mouth of the bottle with the coating surface facing inward. After that, the film was left to stand at 5°C for 1 hour so that the water would not come into direct contact with the coating film, and then the appearance of the film was visually inspected.
<Evaluation criteria>
○: No condensation on the film ×: Condensation on the film

Peel strength (adhesion)
The coating surface of the evaluation laminate film was heat-sealed to a 25 μm thick A-PET film at a temperature of 130° C. and a pressure of 0.2 MPa for 1 second. Then, a 15 mm wide test piece was cut out and subjected to a 180° peel test at a tensile speed of 200 mm/min using an Autograph AG-Xplus manufactured by Shimadzu Corporation at 25° C. to measure the peel strength.
<Evaluation criteria>
◎: 7N/15mm or more ○: 5N/15mm or more but less than 7N/15mm △: Less than 5N/15mm ×: Material breakage

Synthesis of Polyester Resin (A-1) In a reactor equipped with a stirrer, thermometer, heater, cooling device, and distillation condenser, 373 parts by mass of dimethyl isophthalate, 71 parts by mass of 5-dimethyl sulfoisophthalate, 458 parts by mass of diethylene glycol, and 0.2 parts by mass of tetrabutyl titanate were charged, and the mixture was heated to 220 ° C. while carrying out a transesterification reaction over 3 hours. Thereafter, the temperature was lowered once to 150 ° C., 49 parts by mass of sebacic acid was added, and the mixture was heated again to 220 ° C. while carrying out an esterification reaction over 4 hours. After completion of the esterification reaction, the pressure inside the system was raised to 270 ° C. while reducing the pressure to 10 torr over 60 minutes, and further reduced to a vacuum of 1 torr or less, and a polycondensation reaction was carried out at 270 ° C. until the predetermined viscosity was reached. After completion of the reaction, the polyester resin was removed and cooled to obtain polyester resin (A-1).

Synthesis of Polyester Resins (A-2) to (A-10) and (B-1) to (B-9) As in the synthesis example of polyester resin (A-1), polyester resins (A-2) to (A-10) and (B-1) to (B-9) were obtained by changing the types and blending ratios of raw materials as shown in Table 1.

Example 1
Production of aqueous coating composition (A-1) Polyester resin (A-1) was dispersed in water according to the following procedure. 206 parts by mass of polyester resin (A-1), 4 parts by mass of silica particles (powder, particle size 3 μm, pore volume 0.6 ml/g), and 490 parts by mass of water were charged into a reaction vessel equipped with a stirrer, condenser, and thermometer, and the mixture was stirred at 80°C for 1 to 3 hours. After cooling to room temperature, the mixture was removed from the reaction vessel to obtain aqueous coating composition (A-1).

Examples 2 to 10, Comparative Examples 1 to 9
In the same manner as in Example 1, polyester resins (A-2) to (A-10) and (B-1) to (B-9) were used to obtain aqueous coating compositions (A-2) to (A-10) and (B-1) to (B-9), respectively.

Table 1 shows the polyester resin compositions, physical properties, and evaluation results for various characteristics of Examples 1 to 10 and Comparative Examples 1 to 9.

As is clear from Table 1, the aqueous coating compositions of Examples 1 to 10 all achieved excellent water dispersibility, moisture resistance, anti-blocking properties, anti-fogging properties, and adhesive strength. On the other hand, the aqueous coating composition of Comparative Example 1 lacked anti-blocking properties due to the absence of added inorganic particles. Furthermore, the aqueous coating compositions of Comparative Examples 2 to 9 were deficient in one or more of the physical properties due to differences in the composition ratio of the polyester resin or differences in glass transition temperature.

Laminate films coated with the aqueous coating composition of the present invention exhibit excellent water dispersibility, moisture resistance, anti-blocking properties, anti-fogging properties, and adhesive strength when heat-sealed as lids for packaging containers. Furthermore, because no anti-fogging agents are used, the composition exhibits excellent recyclability when applied to thermoplastic resin films. Therefore, the aqueous coating composition of the present invention is extremely useful in the food packaging container industry.

Claims (9)

An aqueous coating composition containing a polyester resin (A) and inorganic particles (B), wherein the polyester resin (A) satisfies the following conditions (i) to (iii):
(i) Among the polycarboxylic acid components constituting the polyester resin (A), the polyester resin (A) contains 60 to 88 mol % of an aromatic polycarboxylic acid component having no sulfonic acid group, 8 to 20 mol % of an aromatic polycarboxylic acid component having a sulfonic acid group, and 5 to 20 mol % of an aliphatic polycarboxylic acid component and/or an alicyclic dicarboxylic acid;
(ii) the polyhydric alcohol component constituting the polyester resin (A) contains more than 50 mol% of a glycol containing an ether group;
(iii) The glass transition temperature of the polyester resin (A) is lower than 20°C. The aqueous paint composition according to claim 1, wherein the reduced viscosity of the polyester resin (A) is 0.2 to 0.7 dl/g. The aqueous paint composition according to claim 1, wherein the inorganic particles (B) have a particle size of 1 to 30 μm and a pore volume of 2 ml/g or less. The aqueous paint composition according to claim 1, characterized in that it does not contain a curing agent. A laminated film characterized by being formed by applying the aqueous coating composition described in any one of claims 1 to 4 to at least one surface of a thermoplastic resin film. The laminate film according to claim 5, wherein the thermoplastic resin film is a PET film. A packaging material having the laminate film described in claim 6 as a component. A lid material for a food packaging container having the packaging material described in claim 7 as a component. A food packaging container having the lid material described in claim 8 as a component.